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sublunacy, I'm not an expert, neither of the 70 cc nor the 90 cc cylinders - but you ARE, as you've got your diploma and years of experience I'd say I don't even have a small piece of your knowledge on 2-stroke engines and I really appreciate that you want to share it here with us

Just wanted to show you that the pipe is really big. I'm not planning the 90 cc kit, I'll stay with the 70 cc. Just mesured the restrictor from the Tecnigas Silence Pro - its diameter is only 13 mm... But we both know what for restrictors are in that kind of exhausts Got my hand on the old stock pipe - it's 21 mm.

Depending on the shop, for the 70 cc cylinder they propose 17,5 up to 21 mm carbs.

I know I'm getting it from the back, but now we know that the exhaust won't block the engine The 70 cc cylinder will be able to evacuate the gases with no problem Now I have to figure out how to get the right amount of the air into the carb, and then, the mixture from the carb to the cylinder

As for the carb, I'll just buy the diameter I'll find with automatic choke and oil intake from the range 17,5 - 21 mm

Going further on from the carb, that's the only intake I've found, that would match the Dellorto 17,5 - 19 mm carbs (haven't check yet what's the intake diameter on the 21 mm carb). It's 2 pieces depending on the needed final diameter, I hope that putting both together will make approximately 90 degrees to get the carb in an appropriate position. Though I've seen a few days ago on an Italian website (could be Dellorto's) that it can be leant up to 40 degrees to the side. Got it in my bookmarks, I'll post it when I'll get to it later

if it were me doing a 90cc i would use a full circle crank and reed spacers. a couple 1/4 inch reed spacers and try to tune the power back with those till the powerband is not to early or to late.... the 90cc kits blow my mind. i just worry about the cranks....

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so i mean theres 2 ways to do this - a sport cylinder with the stock crank or a very expensive midrace cylinder and matching crankshaft.
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i recommend a top performances 2plus 80cc cylinder and crankshaft. its really important you buy the right clutch for good takeoff. if you miss it by 1000rpm to high or to low it will totally suck.

the carbs for these little motors are a pain to tune....the smallest dellorto phbg is like 17mm i think and it fits that intake your looking at for the phbg 19-21.

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i think barrel carbs will be the way to go in the future. the largest barrel carb is 15mm now. perhaps that could be the missing link to a simple build that is both cheap and completly adjustable......
i suggest looking into that and pair it with a cheap 70cc cylinder. give it a go

The guys tested for example my exhaust on my cylinder And others, too. A good comparison getting some light on my stuff.

I'm staying with the 70 cc Malossi kit. And my derestricted exhaust The cylinder is on its way. But still haven't decided about the carb. In order to do so, I took apart the air box and I'm trying to figure out how much more air will my new engine need. The air box looks like that inside. First observation - the filter is doing fine, as you can see, there is no dust on the clean side of the box. The snorkel diameter is 18 mm, which is 50% more than the stock carb size. Logically I should upgrade the snorkel to 25 - 28 mm (depending on the size of the carb), and eventually also the tube going from the airbox to the carb (as for now, it's around 25 mm, so double the size of the carb). Instead of drilling holes in the box, perhaps I simply shall maintain those ratios?

I got my hands on Bell's Performance Tuning book. A excellent book that explains everything. Have to finish it quickly to take a good decision about the carb and eventually also reed size. I remember that some 20 years ago I had my car engine blueprinted by a workshop. I adored the result, even though the changes were only slight. I'll try to take care of my Bella engine now...

sublunacy, I've got an impression that we are not looking at the same graph... Or I am completely unable to read it... The closest one to my setup is this one. I know - we don't have an idea of what the carb, reed valve and the flywheel where used during the test. We can assume it was stock. But still - not much info about the model year of the scoot. I'll try to figure it out

What I can see is that the tested Yasuni and LV pipes aren't delivering any more power than the Tecnigas Silent Pro until 7350 rpms. I know the graph starts only at 6500, but the Yasuni Z makes it around 1 HP less than the Silent Pro at 6500 rpm, and all the tested pipes start on the graph at around the same power level, which is by the way even more than the peak power of the stock engine. Please, do remember that I'm NOT looking for a race scooter Both my pipe, Yasuni Z and LeoVince TT achieve the same power of 7 HP at around 7700. Still looking at the graph I can see that the tested set (Malossi Sport 70 cc + Tecnigas Silent Pro) delivers between 6,5 and 7,5 HP in the range between 7400 and 9300 rpm, which sounds not bad to me. Though I can't find how is my stock engine is set up Yet...

As I can see it, the idea would be to tune a variator in a way to keep those rpms most of the time, to take advantage of the set. I'll think about it when the set will be installed, as those operations can be done on the scooter.

Second point is of course blueprinting - which as I understand is eliminating the inaccuracies of mass production and accountants' need to unificate parts between different models. If I find some extra free time, I'll try to eliminate the existing obstacles on the way of gases both on the intake and exhaust sides of the engine.

Third thing - and the most important for me now - is choosing the correct carb that will suit the cylinder / pipe set the best it can and a matching intake, event though it seems that it could be the most difficult thing. I'm still waiting for a couple of replies from the shop to confirm some points before placing the order (carb, intake, eventually reed valve, but for the last one, no idea what to pay attention at...). If I won't get any positive answers, I'll just have some make me a custom made intake For example in stainless steel. Or aluminium

As for your 2nd post - I know it's not a racing pipe. I wasn't looking for one. At the moment I bought it I was looking for a pipe that will look close to original one, fit underneath the body panel (I think that you are aware of how the Habana / Mojito look like - if not, there's a photo of my Bella in my album - from the right side) and will be quiet and of decent quality. The need to upgrade the set came after taking the cylinder / piston of the engine... But the requirements to the exhaust haven't I know that starting the upgrade from the exhaust isn't logical, I also know that choosing that kind of exhaust wasn't the best choice for tuning, but I do have priorities, as I use my scooter daily. And I simply want to get the rest to match the best what I already have

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it seems from the 70cc dyno image that you dont need a clutch at all. the peak power is at perfect rpms for a stock variator. even thou the pipe manifold is very large the cylinder outlet is just 19mm - to reach full overrevs subtract 20 percent cfm on the cold side - this is a little bigger than the peak power needs in cfm...... you can go smaller but then you will lose a little power everywhere im sure from pumping loss.

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it is a great pipe like i said a week ago. the 50cc dyno image is pretty easy to beat / on a 70cc its right up there with the best!

70cc
vforce reed valve
boost bottle
brand name carb 16-17mm.
foam open filter
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you can blueprint the 70cc cylinder. the cases will have to wait to be blueprinted when you take the cases apart.

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i cant tink of anything else. the boost bottles do work - it just cruises at part throttle better/ better clutch dumps/better overrevs. they do nothing for full throttle at peak power rpms... it just fixes the dodgy parts of the output about 5 percent.

The boost bottle was another part that was going through my mind several times, I was asking myself if / how does it work and what to pay attention at. Of course I've read a few infos on the internet, but it's some kind of equipment I do not have even a bit of experiance with... I found two or three types of them: Malossi, Stage6 and Polini. Of course there are other producers, but as you can see, those three are examples of two (or three) different types of boost bottles. The Stage6's is a solid metal container, the Polini's a little less solid plastic container, and the Malossi's look like an expandable container, though I think it will be fully expanded just on the spring itself and not expand under mixture pressure. Which type will be best? and why? The Stage6's looks of course best, but I don't care, it will be covered by the body panels

Looking at the engine, I'm not sure that I'll have much space for it under the body panels. I think the bottle will be installed with the body panels on And it's quite possible I will take the smalest one

VForce reed valve? On their US website they even don't have such category as scooter... As it's extremely easy to change it on the scooter, I'll look for it later on. Now I'll install the stock one, with carbon petals from the Malossi kit, and lift it up a few milimeters, depending on how it will look when the carter will finally be halved

well...dont mean to hijack the thread but my run in was not successful...i have to open it up to see exactly what failed but i suspect its due to the stock carb Keihin PWS 12mm with an 80 main jet...prolly too small...i will update

jixaw, feel free to post here, as we are only three to discuss, there's no need to follow two different threads
What do you mean by saying that the run in wasn't successful? You've seized the engine? Hope not.. and hope you'll find the exact cause

I got a call today that the kit's delivery will be postponed to Monday I'm going to get the engine silent-blocks (the old ones were damaged) on Saturday and hope to find an exhaust guy that will make for me a custom intake in stainless steel I've had enough of looking for one that will fit.

Just wanted to pop in and say that if your reed valve has the 4 bolt pattern where the holes are off-center like other Morini's, then you can use any of the options from the Minarelli engine. The intake manifolds will work as well. The dyno chart for the exhaust testing is for a different engine, so the hp numbers will be different, but the power curve will be very similar. "How does a Boost Bottle improve performance? Air rushes thru the carb on the intake cycle. Ignition accelerates the piston down, forcing the reeds to snap shut. The momentum (inertia) of the air has to go someplace. It goes back thru the carb causing a double rich mixture. The result can be rough idle or hesitation.

Due to the high velocity of the fuel air mixture through the carb boot, we need to take advantage of this momentum/inertia energy. The Boost Bottle and tube provide storage for the fuel air mixture between carb boots. The energy (pulse) forces the pre-atomized mixture in the tube from the previous cycle into the adjoining carb boot where the reeds are just opening and ready to receive the fuel air mixture. The boost bottle and tube provide a "boost" supercharge effect to each cycle.

The boost bottle is most effective at lower and mid-range rpm, and, when you are on & off the throttle. It assists in filling the cylinder (shorter distance) for a fraction of a second until the carburetor venturi gets enough velocity to fully atomize the fuel. The advantage is that it brings up the torque and horsepower in the bottom of the rpm range, up to where the pipe(s) starts to work. There is a small benefit at high rpm's. " 2-Stroke-Porting.com

Does it actually work? It depends on how modified your engine is. Some people swear by them, some people say they are a waste of money. I can tell you that some of the older 2 stroke snowmobiles came stock with them.

jixaw, feel free to post here, as we are only three to discuss, there's no need to follow two different threads
What do you mean by saying that the run in wasn't successful? You've seized the engine? Hope not.. and hope you'll find the exact cause

I got a call today that the kit's delivery will be postponed to Monday I'm going to get the engine silent-blocks (the old ones were damaged) on Saturday and hope to find an exhaust guy that will make for me a custom intake in stainless steel I've had enough of looking for one that will fit.

I'm keeping the fingers crossed for you

guy...welcome to the forum! stick around!
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jixaw is trying to get a new carb too. hes been stranded trying to get to work a few times before. my point is your both looking for carbs.

i understand the intake manifold to carb to airbox is difficult to pull off with a larger carb to the point where - if you use a larger carb and intake manifold the airbox does not fit anymore. right?

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this is my idea.
since a 16mm carb is perfect for a 19mm cylinder outlet in thermodynamics< it will be the best all around carb size. it WILL reach 9500rpm wich is a 1000rpm beyond what you need.
with that said im suggesting a dellorto phva 14mm. it is a stock carb on 70-80cc 2 strokes that stay under 9000rpm. the tomos a55 engind and the comer 80cc engine for example.
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it would be torquey and easy to jet/tune since you use it all. its quieter than a bigger carb so i think just a foam open filter to top it off. no airbox needed.
the phva 14mm has the electric choke/ vacuum tap/ 90 degree cable/ oil injector tap. everything you need for 136 dollars american.....
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i would prefer a cheaper 15mm carb with all those features but i think you will find others lack the features. yes a 16mm would work - but you wont use it all on your torque pipes. i cant imagine a 14mm carb with open filter will be very loud. you just cant deliver much sound thru a 14mm hole.... deep notes wil not make it out of the carb period. should makes a nice z sound maybe....

im not sure what happened to my top end..i dont think its a seizure but i suspect a ring is broken...i was riding to work and all of a sudden there was a loss of power and it sounded weak...i was coasting to a stop light...i gave it gas to move up to the stoplight and i heard a terriblle rattling sound coming from the motor..i stopped the scoot and had to walk to work....walked it home and plan to tear it apart this weekend......either way its a bummer.....my replacement kit has arrived..this time i got a new wristpin bearing and that larger jet

I dont think the stock carb is going to be viable in the long term for the 70cc....i have been looking at a 14mm delloroto PHVA ....i will probably get one...i just need to be sure i can account for: fitting a new intake manifold for a morini....the vacuum and oil lines dont connect to the stock carb, they goto the engine.....im guessing i would just plug off those inlets on the carb....

I think im going to try to break in the new 70cc with my stock carb (larger main jet - 88) before i try to tune a new carb while running in....i welcome thoughts on this.....

I got a new wristpin bearing as i mentioned....how do i install this? i worry that my hamfisted approach will damage the rod